1. Field of the Invention
The present invention relates generally to a mask used in an exposure apparatus, and more particularly, to a mask for estimating aberration in a projection lens system of an exposure apparatus.
2. Description of the Related Art
Typically, an exposure apparatus is used to form photoresist patterns on a semiconductor wafer in the manufacture of semiconductor devices. Specifically, the exposure apparatus is used to realize patterns on a mask on a photoresist layer. A projection lens system, which reduces and projects patterns on a mask on a semiconductor wafer using light characteristics, is installed in the exposure apparatus. Thus, an estimation of aberration in the projection lens system of the exposure apparatus is necessary.
Referring to FIG. 1, a conventional method for estimating aberration in a projection lens system of an exposure apparatus can best be seen. The mask 11 for estimating is divided into a portion marked with the letter xe2x80x9cKxe2x80x9d. FIG. 2 is an enlarged view of the section xe2x80x9cKxe2x80x9d of FIG. 1 and shows where a lens array 19 and a transparent layer 21 are formed.
In FIG. 1, reference numeral 13 denotes the mask plane (i.e., mask surface). Light emitted from a light source in the exposure apparatus passes through lenses 16a and 16b of a projection lens system 15, and image patterns are formed on an image plane 17 of a semiconductor wafer.
Light Axe2x80x2, Cxe2x80x2, Exe2x80x2, Axe2x80x3, Cxe2x80x3, and Exe2x80x3 passing through a portion of the mask 11 in which the transparent layer 21 is not formed creates reference pattern 23 with respect to the entire projection lens system 15 in the image plane 17. Light A, B, C, D, and E traveling through a portion of the mask 11 in which the transparent layer 21 is formed, passes through a desired position of the projection lens system 15 through a pin hole 25 of the transparent layer 21 and forms measurement pattern 27.
In particular, light marked D in FIG. 1 is light passing through the projection lens system 15 without aberration, and light marked Dab is light passing through the projection lens system 15 with aberration. The aberration is estimated by comparing the reference pattern 23 with the measurement pattern 27. In FIG. 1, reference numerals 29 and 31 denote an aperture plane and an aperture stop, respectively.
The lens array 19 should be manufactured at the backside of a mask that is used in the conventional method for estimating aberration in the projection lens system of the exposure apparatus. In addition, the transparent layer 21 in which the pin hole 25 is formed should be manufactured at the front side of the mask. Further, it costs a great deal to manufacture the mask used in the conventional method for estimating aberration in a projection lens system of an exposure apparatus. Consequently, it is therefore desirable to provide a mask for estimating aberration in a projection lens that overcomes the disadvantages of the known prior art.
At least one exemplary embodiment of the present invention provides a mask for estimating aberration in a projection lens system of an exposure apparatus by changing mask patterns.
In at least one exemplary embodiment of the present invention there is provided a mask for estimating aberration in a projection lens system of an exposure apparatus. The mask includes a mask substrate and mask patterns arranged on the mask substrate such that a critical dimension (CD), represented by the width of each of the mask patterns, and a phase of the mask patterns have a size proportional to a SINC function. Preferably, the distance between the centers of the mask patterns is substantially uniform. The phase of each of the mask patterns may be provided by etching the mask substrate.
According to at least one exemplary embodiment of the present invention, the size and phase of light transmitted to the projection lens system during an exposure step are substantially uniform, and thus an aberration value in each portion of the projection lens system depending on each mask pattern is not distorted and is uniform.